For most people, belly fat is an insulin resistance issue. The post menopausal pouch is exactly that, excess fat brought on by the onset of insulin resistance in the fat cells of the belly. In terms of whole grainsthe real benefit seems to come from beta glucan, which promotes better post eating insulin function ( you burn carbs better instead of store them) which points to oats. Wheat actually seems to influence stomach distention (which is why some people who eat wheat get a bloaty stomach). Interestingly, intact wheat kernels ( not cracked wheat) seem to dramatically reduce the insulin response after a meal

Oatmeal is classified under whole grains, do you think regular consumption of oatmeal helps reduce belly fat? which is more preferred the one that needs cooking or the instant? are there really differences between the two in terms of their effectiveness?

Anything that comes from it's most natural state is going to have a higher benefit compared to something that has already been precooked/steamed and then packaged for convenience. It is my understanding that it healthier to eat regular oats compared to instant.Instant has a higher Glycemic load. Glycemic load is when it measures how a particular food impacts blood sugar and insulin. The higher the glycemic load (GL) number, the more impact a food has on insulin release. The scale is from 1-50 pure glucose having a GL of 50. "Instant"unsweetened oatmeal 17 versus regular oats GL 13----you can typically decrease the GL by adding almonds or whey protein. Hope this helped!!